Quarterly Financial Data Items affecting quarter results (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2014
Loss on settlement of foreign currency forward purchase, net of tax				$ 11.6
After-tax business development and related costs	$ 1.7	$ 1.3	$ 0.5	9.5	$ 1.0	$ 0.5	$ 1.0	$ 0.7
After-tax credit facility refinancing-related costs				1.3			2.9
After-tax gain on sale of assets	0.2	0.9	$ 0.3	0.2	1.0	0.9	$ 1.0	$ 0.5
Adjustment for tax returns from previous fiscal year		$ 0.4
Tax benefit associated with the United States Short Line Tax Credit	27.4				27.0
After-tax out of period impact of final allocation of fair values to assets and liabilities	1.6
Tax benefit from retroactive change in tax accounting method related to acquired companies						3.9			$ 3.9
Tax benefit related to final tax returns filed						$ (0.7)
Income tax expense due to the application of the full year effective tax rate	1.3				$ 3.5
Australian Operations [Member]
Severance costs, net of tax				$ 1.2
Foreign Tax Authority [Member]
Tax benefit from tax rate adjustment	$ 9.7